Film



Patented- Apr. 2 8, 1942 Daniel D. Lanning, Williamsville, N. -Y., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application January 2, 1940, Serial'No. 312,096

12 Claims.

The invention relates to the stripping of dry cast cellulosic films, especially continuous webs, from the casting surface. More particularly it appertains to the incorporation of materials such as ammonium oleate, for convenience called stripping agents, in organic solventsoluble organic cellulose substitution derivative dopes for facilitating separation of the cast film from the casting wheel.

Cellulosic materials which have been applied inorganic liquid solution to the surface of such materials as wood, metals, ceramics, plastics and the like, and the solvent evaporated, possess considerable adhesion therefor. Such an inherent adhesion is very undesirable when the base is employed only as a temporary support during the solvent removal as in the casting of self-supporting film such as sheet wrapping and similar material.

In general dry casting procedures involve the laying of a film of dope (solution ofthe cellulose substitution derivative) on to a casting wheel mounted for rotation and arranged for the re- .moval of the solvent from the dope during its rotation. The means for thesolvent removal may include heating the surface of the wheel or $1.11- faces adjacent thereto, together with devices such as fans for carrying the solvent or solventladen atmosphere away from the film. Ordinarily the speed ,of the wheel and the degree of heating are adjusted so that the desired amount of solvent is removed in somewhat less than one revolution of the casting wheel. Nickel, chromium, stainless steel and other metals and al.- loys are generally used for surfaces of the casting wheels.

In attempting to carry out a continuous casting operation of this type with ethyl cellulose dopes, it was found that the adhesion between the partially dried film and the casting surface was a frequent source of trouble. It caused the film to break or tear at the place where the film was being stripped from the wheel. This action was especially troublesome at the edges of the film. Even when the film did not tear or break, distortion and deformation were quite common due to the high tension required for pulling the This invention had for an object the manufacture of transparent, strong,'and flexible organic solvent soluble cellulosic sheets or films which were undeformed and/or undistorted and/ or unmarred, and the production of compositions of matter suitable for the casting thereof. A further object was to dry cast toluene-ethanol 20) soluble ethyl cellulose into thin, strong, smooth, flexible sheets capable of being easily stripped from the casting wheel while retaining 5% to 15% of the solvent of the casting dope. Further objects were to devise a means of decreasing the adhesion between a dry cast, or-

ganic solvent soluble organic cellulose substitu tion derivative and the casting surface, to facilitate the removal of partially dried, dry cast, cellulose substitution derivatives from casting wheels and belts, and to find materials which could be added to cellulosic dry casting solutions to make removal of the film easy when only a small proportion of the solvent remains. A general advance in the art, and other objects which will appear hereinafter, are also contemplated. V

' It has now been discovered that the inorganic salts of fatty acids containing more than 6 carbon atoms, may be incorporated in organic cellulose substitution derivative dry casting dopes with the result that the film formed therefrom can be easily and satisfactorily removed from the casting surface.

From the following description and specific examples, in which are disclosed certain embodiments of the invention as well as details of what is believed to be the best mode for carrying out the invention, it will be apparent how the foregoing objects and related ends are accomplished. The parts are given by weight throughout the application, unless otherwise specified.

Example I A solution containing 15% ethyl cellulose, 15% (on the basis of the ethyl' cellulose) di-amyl phthalate and 2% (based on the ethyl cellulose present) sodium oleate dissolved in a tolueneethanol 80:20 solvent mixture, was prepared. The sodium oleate was dissolved in ethanol, the resultant stirred into toluene and the other nonvolatile materials incorporated in the resulting solution. Film was cast from this homogeneous solution onto a nickel surface and dried thereon. It possessed only a slight adhesion to the nickel surface, as compared to film cast from a similar solution to which no sodium oleate had been added. Equivalent results were obtained with other plasticizers, for example, tri-butyl phosphate, tri-ethylene glycol hexoate and butyl phthalyl butyl glycolate.

Example II A film was prepared from a dope consisting of 15% of benzyl cellulose, together with 15% (based on the benzyl cellulose) di-butyl phthalate and a solvent consisting of a toluene-ethanol 80:20 mixture. Into this dope there was uniformly incorporated 2.5% (based on the solids content of the dope) calcium oleate. The calcium oleate dissolved readily therein. The resulting material was cast on a stainless steel casting wheel, and all but 5% of the non-solids '(the toluene-ethanol mixture) was evaporated,

and the resulting film stripped from the casting wheel. It stripped very easily compared with a similar film containing no stripping agent. The V film obtained was highly transparent and durable. The results obtained with the sodium and calcium salts of lauric acid, myristic acid, palmitic acid and oleic acid indicate that such salts are especially suitable for the present invention.

Example III A dope was prepared consisting of ethyl cellulose together with 15% (on the basis of the ethyl cellulose present) butyl phthalyl butyl glycolate, and a solvent consisting 'of an ethylene dichloride-isopropyl alcohol 80:20 mixture. To this dope there was added 2% (based on the nonvolatile materials in the dope) of calcium oleate.

A thin layer of this dope was cast on a nickel casting wheel and the volatile solvent evapo- A dope consisting of 17% of ethyl cellulose (48.0% ethoxyl content) together with 15% (on the basis of the ethyl cellulose) tri-butyl phos-\ phate and a solvent consisting of an 80:20 mixture of toluene-ethanol, was cast in a continuous manner upon the polished surface of a large diameter chromium-surfaced drum. Before casting 3% (based on the film-forming material and plasticizer content) of ammonium myristate was incorporated in the dope. Upon evaporation of the solution, a highly transparent and durable film was obtained, which was easily (compared with the same composition when no stripping agent was present) stripped from the casting drum. Similar results were obtained with related ammonium fatty acid salts, such as the laurate, palmitate, oleate and stearate. The results obtained with the ammonium oleate were ated similarly to the ethyl cellulose.

' Example V V A film was prepared by evaporating the solven from a composition consisting of 15% ethyl cellulose together with 15% (based on the ethyl cellulose) plasticizer and an 80:20 mixture of toluene-ethanol, in which had been incorporated easily carried out. Similar'results were obtained with ammonium soap.

Example VI To a solution containing 20% ethyl cellulose dissolved in an 80:20 toluene-ethanol mixture, was added 3% calcium laurate (on the basis of the ethyl cellulose). Film cast from this solution onto a nickel surface and dried to 8%-10% solvent content possessed only a slight adhesion to the nickel surface, when compared to ,film cast from a similar solution to which no' calcium laurate had been added. Similar results were obtained with the strontium, barium, lithium and zinc laurates.

Example VII A dope consisting of: Per cent Benzyl cellulose (52% benzyloxy content)- 10 Ethyl cellulose (48.0% ethoxyl content) 5 Di-butyl phthalate 3 Tri-butyl phosphate 1 Ethanol 20 Toluene 80 in which had been incorporated 2% (based on the cellulosic components) lithium palmitate, 1% zinc oleate and 1% calcium myristate, was cast continuously on the polished surface of a rotating nickel cylinder six feet in diameter. The volatile materials were evaporated, and the resulting film stripped from the surface of the casting wheel. The film, which had a thickness of .00088 inch, was very clear, and had excellent tear resistance. It was undeformed, unmarred, and undistorted. It was'stripped from the casting wheel very easily. Similar results were obtained with related mixtures.

The dope or cellulosic material solution containing the strip agents of the invention may be handled and cast in the same manner as the dry casting dopes previously known to the art.

The most marked decrease in adhesion between the film and the casting wheel surface has been noted when the casting surface was nickel.

In the. preferred mode of operation the film is stripped from the casting wheel while it still contains 5% to 15% of the solvent. In all cases the major portion of the solvent should be removed before stripping the film.

This, invention. is not limited to the ethyl cellulose of the specific examples, although it peculiarly appertains thereto, In general it is,

' very outstanding. Ethyl benzyl cellulose operwith considerable efficacy, applicable to all kinds of cellulosic compounds which are soluble in organic liquid "(solvents), including cellulose esters such as cellulose acetate, cellulose propionate, cellulose butyrate and the like; mixed esters, such as cellulose aceto-propionate, cellulose aceto-butyrate and the like; cellulose ethers,

such as methyl cellulose, ethyl cellulose, propyl cellulose, butyl cellulose, benzyl cellulose and the; like; mixed ethers, such as ethyl benzyl cellulose and the like; and mixed cellulose etheresters such as ethyl cellulose acetate and the like.

Many plasticizers for dry cast cellulosic film have been suggested heretofore, and sincethe stripping agents of the' invention are generally compatible therewith, it is only necessary to point out that the film may be plasticized in the conventlonal ways, if desired.

The inorganic salts of fatty acids suitable for use in the operation of this invention, that'is,

for decreasing the adhesion between the dry cast film and thesurface In certain cases the calcium salts of the fatty acids are preferred when reduction of water (or moisture) sensitivity in the cellulosic film is desired. The employment of ammonium oleate has been found to be especially desirable.

In the preferred embodiments of the invention the stripping agent is present in an amount within the range of 0.5% to by weight on the basis of the cellulosic material. Higher concentrations are not excluded. and may be used in order to secure specific results.

The strip agents may be used singly or in any combination, for example, ordinary sodium soap, and the invention is not limited to the specific materials listed above or in the specific examples.

The stripping agents of this invention may be soluble organic cellulose substitution derivative film from a metal or alloy casting wheel at elevated temperatures, and that all danger of tearing or deforming the ping point (or line) separate the film from the casting surface has been removed.

calcium, mag- 1t 18 to be limited to the specific embodiments thereof ex- As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, understood that this invention is not cept as defined in the appended claims.

I claim:

1. A plasticized, organic solvent soluble ethyl cellulose film, containing 0.5% to 5% of ammonium oleate.

2. A dry cast film of ethyl cellulose containing 0.5% to 5% of an ammonium soap.

3. Organic solvent soluble ethyl cellulose sheet wrapping material containing 0.5% to 5% ammonium salt of fatty acid; said fatty acid containing 12 to 20 carbon atoms.

4. An organic solvent, dry casting solution of cellulose substitution derivative containing, as a strip agent, ammonium oleate.

5. An organic solvent dry casting solution of cellulose substitution derivative containing, as

The advantage of incorporating in a casting solution a material which between the cellulosic film cast therefrom and the casting surface without undesirably affecting the transparency and surface characteristics of the film, will be obvious to those skilled in the art.

decreases the adhesion strip agent, ammonium fatty acid salt in which the fatty acid radical contains at least 7 carbon atoms.

6. Organic solvent wrapping material containing 0.5% to 5% strip agent consisting of in which the fatty acid radical contains 12 to 20 carbon atoms and 5 o to 15% casting solvent.

7. A dry cast cellulose substitution derivative sheet wrapping material containing 0.5% to 5% ammonium soap.

8. A dry cast cellulose substitution derivativesheet wrapping material containing 0.5% to 5% ammonium oleate.

9. A dry cast cellulose substitution derivative sheet wrapping material containing 0.5%

and 5 to 15% of the casting solvent for the cellulose substitution derivative.

10. A dry cast cellulose substitution derivative sheet wrapping material containing 0.5% ammonium fatty acid salt in which the acid radical contains 12 to 20 carbon atoms.

' 11. A dry casting cellulose substitution derivative solution containing ammonium soap.

12. A dry casting cellulose substitution deriva tive solution DANIEL D. MN'NING. 

